Percussion tool



July 3, 1956 c. LEAVELL 2,752,889

PERCUSSION TOOL Filed Aug. 5. 1953 INVENTOR. 4 CHARLES LEA VELL ATT URNE Y5 United States Patent O PERCUSSION TOOL Charles Leavell, Lombard, Ill., assignor to Mechanical Research Corporation, Chicago, 111., a corporation of Pennsylvania t Application August 3, 1953, Serial No. 371,957

20 Claims. (Cl. 121--13) This invention relates to percussion tools, and more particularly to paving breakers and the like wherein difficulty is experienced in removing the work member of the tool from a material it has penetrated.

It is well known that there are two distinct phases in the operation of paving breakers. First, the tool is operated in a manner to break a large section of material into smaller pieces, and during this breaking operation the work member of the tool penetrates the. material and in so doing causes a piece thereof to break 013 of the larger section. Secondly, after the work member has penetrated the material to the full extent of its length, or a piece of material has broken away, or the operator determines that it is more desirable to penetrate the ma terial at another point, the work member must be withdrawn or pulled out of thematerial it has penetrated before the tool can again be employed in a subsequent breaking operation. I i

In order to remove the work member from a materialpenetrating position, the operator or workman must pull or lift the tool away from the material so that the easing of the tool moves axially with respect to the work member to bring a casing portion (usually the inwardlyextending ear of a retainer member) into abutting engagement with a portion of the work member (a laterally-extending retaining flange with which the work member is equipped). When this physical relationship between the paving breaker casing and work member is established by an active pull or lift upon the heavy casing by the workman, conditions are proper for the withdrawal or pull out of the work member.

conventionally, paving breakers operate with a considerable amount of vibration, and the incessant vibratory movement of the tool casing is extremely fatiguing for the operator. The vibration is utilized to advantage, however, during the pull out of the work member from material-penetrating position. This results because once the workman has lifted the casing of the tool until the retainer member substantially abuts the retaining flange of the work member and thereafter maintains this physical relation, the upward component of the vibratory motion, or the component of the vibration in a direction away from the material, causes the casing (through the retainer member) to repeatedly impact the retaining flange of the work member and the repetitious impact forces drive the work member from the material it has penetrated.

It is apparent that the vibratory component in a direction away from the material is used to accomplish the work member pull out at the expense of increasing fatigue of the workman, since he must lift the heavy tool casing during the pull out phase of operation and he is therefore tense and his muscles tightened and the full pounding effects of the casing vibration are absorbed by him without attenuation in relaxed muscles. Fatigue is thereby hastened and the workmans efliciency decreases rapidly with the frequency of the pull out operation.

Fatigue of the workman, in addition to bringing about the general decrease in his efliciency, results in his inability to lift the paving breaker casing with suflicient force (often in the nature of about pounds) to bring the retainer member and retaining flange of the Work member into substantially abutting relation. Thus, the speed of the pull out phase of the tool operation decreases because a portion of the force that vibrates the tool casing in a direction away from the penetrated material is dissipated in lifting the casing through a relatively large distance to bring the retainer member and retaining flange into abutting relation and is not, therefore, translated into impact between these two members. Impact force is thereby lost and efficiency of the pull out operation suffers. This condition is particularly serious where the material penetrated by thework member is a heavy concrete slab and the pull out operation is slow at best. With material such as this, often the work member cannot be removed by the customary pull out operation because the frictional forces gripping the work member are in the order of from 500 pounds to 2,000 pounds, and other removal means must be adopted.

There has long been a need for percussion paving breakers and like tools wherein it is unnecessary for the operator to lift the heavy tool casing during the removal of the work member of the tool from a material it has penetrated, and it is accordingly an object of this invention to provide such a tool. Another object of the invention is to provide a paving breaker or the like in which the pull out phase of its operation is quite rapid as compared With conventional tools and in which the tool casing is automatically lifted, when desired, relative to the work member to provide the most desirable positioning therebetween for purposes of the Work members removal from embedded position in the material it has penetrated. A further object of the invention is the provision of impact means selectively operable with the casing lifting means to substantially abut the work member retaining flange when the casing is raised relative to the work member, whereby the full force tending to vibrate the casing in a direction away from the material penetrated by the work member is translated intoimpact against the retaining flange and portions' of this force are not, therefore, dissipated in further lifting of the casing. Still another object of the invention is to provide selectively operable fluid pressure means for lifting the paving breaker casing relative to the paving breaker work member and establish therebetween a physical relationship for purposes of achieving eflicient and rapidremoval of the paving breaker work member from embedded position in the material it has penetrated and without the requirement of the workmans lifting the tool casing. Yet a further object resides in providing a fluid pressure actuated impact pin automatically actuated upon operation of the fluid pressure lifting means for impacting the retaining flange of the work member upon movement of the tool casing during the portions of the vibration when the casing moves in a direction away from .the material penetrated by the work member.

Yet a further object is to providemeans whereby the actuation of the impact pin does not occur until the casing of the paving breaker has been lifted to its maximum position relative to the work member, and in which the impact pin is deactuated prior to the return of the casing to its normal lowered position. Still another tobject is to accurately position the impact pin relative to the retainer member whereby the tool operates in a conventional manner without danger of breakage of "the retainer member uponmovement of the work member and wherein the impact pin is also positioned relative to the work member retaining flange so that efiicient pull out of the tool is accomplished by the impact between the retaining flange and impact pin, as hereinbefore described. Additional objects and advantages will appear as the specification proceeds.

An embodiment of my invention is illustrated in the accompanying drawing, in which a longitudinal sectional view is shown.

The paving breaker illustrated is for the most part conventional and includes a casing having a front head portion 10a, tappet seat portion 10b, cylinder casing portion 100, and rear head portion 10d. The rear head 10d is equipped with a pair of laterally-extending handles 11, and mounted above one of the handles 11 is an actuating lever 12 adapted upon movement to open the valve 13 to admit pressure fluid through the supply fitting 14 from a suitable pressure fluid source (not shown). A valve assembly designated generally by the numeral 15 is operative to direct the flow of pressure fluid alternately through passage 16 and port 17 into the lower portion of the cylinder 18 and then through the inlet port 19 to the upper end of the cylinder 18. This valve and its operation are conventional and a detailed description is therefore believed unnecessary. It is suflicient to say that the valve is cyclically operable to first cause the flow of pressure fluid into the cylinder 18 adjacent the lower end thereof and then into the cylinder 18 adjacent the upper end thereof.

Slidably mounted within the cylinder 18 is a piston or hammer 20 that reciprocates within the cylinder 18 upon application of the pressure fluid to opposite ends of the cylinder. Mounted intermediate the ends of the cylinder 18 is an exhaust port 21 that is operative to exhaust opposite ends of the cylinder 18 as the hammer 20 reciprocates therein.

Slidably mounted in a chamber 22 provided by the tappet seat 10b is a tappet or anvil (sometimes referred to as a pedestal) 23. The tappet 23 has a relatively small upwardly-extending portion 24 that is adapted to extend into the lower portion of the cylinder 18 for receiving impact blows from the hammer 20. The tappet 23 also has an enlarged lower or body portion 25 formed integrally with the reduced portion 24 and connected thereto by a relatively large inclined shoulder 26. The inclined shoulder 26 engages a frusto-conical shoulder 27 provided by the tappet seat member 10b when the tappet 23 is in its uppermost position. The tappet 23 translates impact force from the hammer 20 to a work member 28 slidably mounted within the front head 10a of the tool casing. The work member 28 is free to slide axially within the casing and upon impact of the hammer 20 against the tappet 23 the work member 28 is driven by the impact and moves a small distance relative to the casing.

The work member 28 is equipped intermediate its ends with an annular retaining flange 29 that slides freely within an enlarged chamber 30 provided by the front head 10a. To prevent the work member 28 from falling from the casing 10, the front head portion 10a of the casing is equipped with a retainer member 31 pivotally mounted upon a pin 32. The retainer member 31 is equipped with an inwardly-extending ear 33 adapted to engage the annular retaining flange 29 of the work member and to thereby confine the work member within the casing. A pin 34 biased by a spring 35 into engagement with the retainer member positions it so that the ear 33 is normally extended into the chamber 30. However, the retainer member 31 may be pivoted in a counterclockwise direction to withdraw the ear 33 from the chamber 30 and to permit the work member 28 to be readily removed or inserted into the position illustrated within the casing.

In the conventional paving breaker so far described, I equip the casing 10 with an axially-extending passage 36. At the junction between the cylinder casingportion 10c and the tappet seat member 10b a branch passage 37 is provided that extends to the shoulder 27 and is in open communication with the chamber 22 provided by the tappet seat member 10b. At its lower end the passage 36 is in open communication with a cylinder 38 having slidably mounted thereon and in sealing engagement therewith an impact pin member 39 equipped with an enlarged head portion 40 and a reduced inwardly-extending impact portion 41. A coil spring 42 normally biases the impact pin 39 in an outward direction so that the reduced impact portion 41 does not extend into the chamber 30 and it does not therefore provide an obstruction engaging the annular flange 29 of the work member so as to prevent free axial movement of the work member. A plug 43 is received within the outer end of the cylinder 38 to provide a seal therefor. The plug 43 may be pressed within the outer end of the cylinder or it may be threadedly received within a threaded portion provided at the outer end of the cylinder. In any event, it is desired that a fluid-tight seal be formed between the plug and outer cylinder portion. It is also desired that the enlarged head portion 40 provide a fluid seal with the cylinder 38.

At its upper end the passage 36 communicates with a valve chamber 44 equipped with a rotatably-mounted valve 45 having a passage 46 therethrough. When the valve 45 is in open position, as illustrated, the valve passage 46 communicates at one end with the passage 36 and at its other end with a short passage 47 that is in open communication with the supply fitting 14. The valve 45 is also provided with a relatively small passage 48 that communicates with the passage 36 when the valve is closed, and when in closed position the end of the valve passage 46 communicates with a relatively small passage 49 extending through the side wall of the casing and com municating with atmosphere. The small passages 48 and 49 are operative in conjunction with the passage 36 and valve passage 46 to exhaust the passage 36 to atmosphere when the valve is closed.

Control of the rotatably-mounted valve 45 is attained through a trigger or lever member 50 equipped at its upper end with a finger grip 51. The trigger 50 is slidably mounted within a channel provided by flange members 52 formed rigidly with the casing walls. A coil spring 53 normally holds the trigger member 50 in lowered position to close the valve 45. The trigger member 50 is equipped at its lower end with a link 54 pivotally secured to a lever 55 pivoted intermediate its ends upon a pivot pin 56 mounted in the casing wall. At its opposite end the lever 55 is slidably and pivotally connected with a crank 57 by means of a slot and pin arrangement illustrated. The crank 57 is rigidly secured to the valve 45 and it is apparent that movement of the trigger member 50 is operative to rotate the valve 45 between opened and closed positions.

Above the junction of the passages 36 and 37, the casing is equipped with a threaded aperture 58 that threadedly receives a threaded needle-shaped restriction member 59. The purpose of the member 59 is to restrict the passage 36 and thereby retard the flow of pressure fluid therethrough. If desired, the member 59 may be adjustable so that the restriction provided in the passage 36 may be altered as required to meet particular situations. The passage 36 may be of relatively small cross section and if desired a conduit might be provided along the outer wall of the casing 10 as an alternative to the passage 36 extending through the casing wall. Such a change, however, would not affect the operation of the structure.

Operation The paving breaker illustrated will be operated in the conventional manner to bring about the breaking up of any given material. The workman will grasp the paving breaker by the handles 11 and position the work member 28 thereof at a point. being the most desirable to commence the Work phase of the operation wherein the work member 28 is driven into the material having work performed thereon. When the workman depresses the valve control handle 12, the valve is opened and pressure fluid flows through the supply fitting 14 and valve assembly 15 alternately to the lower portion of the cylinder 18 through the passage 16 and drives the hammer 20 upwardly in the cylinder 18. Since the pressure fluid exerts forces in all directions, at the same time it is pushing the hammer 20 upwardly it is also pushing downwardly upon the lower end of the cylinder 18 and thereby pushes the casing of the paving breaker downwardly relative to the work member 28 which is either resting upon or is embedded in the material being broken. As the hammer 20 rises in the cylinder 18 and passes above the exhaust port 21, the lower portion of the cylinder 18 is exhausted to atmosphere through the exhaust port and at this moment the valve within the valve assembly 15 is reversed automatically and pressure fluid is discharged into the cylinder 18 adjacent the upper end thereof through the inlet port 19. The entry of pressure fluid into the upper end of the cylinder 18 is operative to drive the hammer 2 0 downwardly and at the same time reacts against the upper end of the cylinder 18 and lifts the casing relative to the work member 28. When the hammer 20 has moved downwardly beyond the exhaust port 21, the upper end of the cylinder 18 is exhausted to atmosphere and the hammer impacts the upper end of the tappet 23 (which will be extending into the cylinder 18) and the impact force will be transferred through the tappet 23 to the work member 28 to drive it a small distance into the material being broken. The cycle is then completed and is repeated about 1200 times per minute. it is seen, then, that the upward and downward movement of the casing occurs very rapidly and is apparent as a vibratory movement that seriously affects the workmans operation of the tool.

When it is desired or necessary to remove the work member 28 from embedded position within the material it has penetrated during the work operation previously described, the workman lifts upwardly on the handles 11 with a force suliicient to raise the casing 10 relative to the work member 28 to bring the ear 33 of the retainer member 31 into abutting relation with the annular retaining flange 29 of the work member (assuming a conventional paving breaker structure, not having the impact pin 39, passages 36, etc, incorporated therein). Where the paving breaker is relatively large, the lift applied to the handles 11 by the workman in order to bring the car 33 and flange 29 into engagement is often in the order of about 150 pounds. This is a considerable force and creates a serious strain upon the workman and the.

effects are amplified since, when strained, he is tense and the muscles are taut and the full effects of the vibratory movement of the paving breaker are absorbed by him. The lift applied to the handles, however, is not suflicient to prevent the casing 10 from vibrating and the upward component of the forces causing the vibration is translated through the casing 10 and ear 33 of the retainer member 31 into impact against the retaining flange 29 of the work member and the work member is thus driven from its embedded position in the work material.

However, with my invention, once the work member 28 is embedded and it is desired to remove the same, the workman does not apply a lifting force to the handles 11. Instead, he simply raises the trigger member 50 to open the valve 45 and establish communication between the pressure fluid supply fitting 14 and the passage 36. Pressure fluid immediately flows through the short passage 47, valve passage 46 and passage 36 to the branch passage 37. The pressure fluid then flows through the passage 37 and into the chamber 22 provided in the tappet seat member 1012 and this pressure is exerted in all directions and forces the tappet 23 downwardly. If the tappet 23 is resting upon the upper end of the work member 28, as

will be the case when the work member 28 is embedded or is resting upon thematerial and the valve handle 12 is released to close the valve 13, the. pressure fluid flowing through the passages 36 and 37, upon opening of valve 45, and acting between the shoulders 26 of the tappet and 27 of the tappet seat member will raise the casing 10 relative to the workmember 28 and tappet 23. The casing 10 will be raised until the tappet member 23 is seated on the lower end of the tappet seat member. This follows because the forces exerted by the pressure fluid within the chamber 22 acts against the casing 10 and the work member 28 (through tappet 23), and since these members are movable relative to each other, the casing raises, the force being sufficient to establish this condition.

It may be pointed out that to safeguard against a workmans pressing downwardly upon the handles 11 at this. time with sufficient force to prevent the raising of the casing 10 relative to the work member, the angular shoulder 27 may be made as wide as required so as to provide a lifting force on the casing of sufiicient magnitude to forestall this possibility. The required width of the shoulder may be easily determined through the relation of force (necessary lift) being equal to the pressure of the pressure fluid times the area of the shoulder. The pressure of the fluid is known and is a constant and the force is a known constant, beingequal to the weight of the casing plus whatever down-push of the Workman it is desired to overcome.

At the same time that pressure fluid flows through the branch passage 37 to raise the casing 10, the pressure fluid also flows through the lower portion of the passage 36 and into the cylinder 38 to actuate the impact pin 39 and. force the reduced end portion thereof outwardly and into the chamber. The actuation of the impact pin 39 will be delayed slightly and will follow behind the lifting ofthe casing 10 for two reasons. First, the spring 42 isselected so that the force exerted thereby to normally hold the impact pin 39 outwardly will require a greater pressure to actuate the impact pin 39 and force it in-- wardly against the biasing action of the spring 42 than the pressure necessary to raise the casing 10 relative to the work member. In other words, if the shoulders 26 and 27 are sufficiently large so that a pressure of 50 pounds per square inch will raise the casing 10 to its maximum position relative to the work member 28, the spring 42 may be selected so that a pressure of 60 pounds per square inch, for example, will be required to actuate the impact pin 39. Secondly, to forestall an instantaneous increased maximizing of the pressure within the passages 36 and 37 upon opening of the valve 45 whereby the casing might be raised and the impact pin actuated simultaneously, the passage 36 above its junction point with the passage 37 is restricted by means of the needleshaped restrictor member 59 so that the build-up of pressure in the chamber 22 and in the cylinder 38 is relatively slow. Therefore in the example set out the pressure in the chamber 22 and in the cylinder 38 would attain 50 pounds per square inch sometime prior to a build-up of pressure equalling 60 pounds per square inch, whereby the casing 10 willbe lifted prior to actuation of the impact pin.

It is apparent that numerous arrangements may be employed to accomplish the relatively slow build-up in pressure within the chamber 22 and cylinder 38, and the restrictor member 59 is exemplary of such devices, the important relationship being that the volumes of the chamber 22 and cylinder 38 and also the branch passage 37 and lower portion of the passage 36 be relatively large with respect to the orifice through which the pressure fluid must flow to establish the required pressure buildup in the chamber and cylinder.

It is desired that the casing 10 be raised relative to the work member 28 prior to actuation of the impact pin so that the retaining flange 29 of the work member is not trapped below the impact pin, 39, which might be the 7 case in the event the impact pin were actuated prior to the raising of the casing. If this should occur, the impact pin would be inoperative to remove an embedded work member.

After the trigger member 50 has been raised by the workman to lift the casing 10 and actuate the impact pin 39, the physical relationship between the various members is as illustrated in the drawing. It is noted that when the casing is in raised position the upper end of the tappet 23 is flush with the lower end of the cylinder 18 and the member 29, when it moves downwardly, will not impact the tappet member 23 so as to drive the work member 28 downwardly. Actually, the hammer member 20 does not normally reach the lower end wall of the cylinder 18, because a quantity of air is trapped below the lower end wall of the cylinder and the inlet port 17 by the downward movement of the hammer and as it moves downwardly, the pressure of the trapped air or air cushion increases to a point sufficient to interrupt the movement of the hammer before it strikes the lower end wall of the cylinder 18. It is apparent also that the lower end of the tappet 23 rests upon the upper end of the work member 28 and this position of course is required to maintain the casing in raised position, for there must be some element apart from the casing 10 against which the pressure fluid in the chamber 22 can react before it can be effective to raise the casing.

The drawing further makes it clear that the position of the impact pin 39 is such that it substantially abuts the annular retaining flange 29 when the tappet 23 is in its lowermost position and is resting against the upper end of the work member 28. Therefore, when the workman depresses the lever 12 to open the control valve 13, the casing 10 vibrates as usual and, as described hereinbefore, the downward component of the vibratory motion moves the casing and impact pin 39 downwardly and away from the retaining flange 29 and the upward component of the vibratory motion moves the casing upwardly and, consequently, the impact pin into engagement with the flange 29. Since this movement is very rapid and occurs about 1200 times per minute, the movement of the casing is rapid and sharp and the impact pin 39 strikes or impacts the retaining flange 29 and, since the impact is of a very short duration, the force upon the flange 29 and consequently upon the work member 28 is relatively large and each impact is effective to drive the work member a short distance from its embedded position in the gripping material it has penetrated.

The casing 10 is maintained in its uppermost position relative to the work member 28 by the lifting action of the pressure fluid in the chamber 22 with the result that a portion of the force causing the upward component of the vibratory motion is not dissipated in lifting the casing and substantially all of this force is translated into impact against the retaining flange 29. The work member 28 is thereby driven from the gripping material it has penetrated very quickly and without necessity of the workmans lifting the casing, while the work member may also be removed from penetrating position in heavy concrete slabs where the friction grip of the material is exceedingly large and could not heretofore be overcome.

Upon removal of the work member 23 from the work matei'ial, the workman releases the lever 12 to close the valve 13 to discontinue operation of the paving breaker and at the same time releases the trigger member 50 to close the valve 45. It is noted that when the valve 45 is rotated to closed position, the small passage 48 is brought into communication with the passage 36 and the valve passage 46 is moved into communication with the small passage 49. The passage 36, chamber 22, and cylinder 38 are thereby exhausted to atmosphere and deactuation of the impact member 39 and lowering of the casing is insured.

The restriction in the upper portion of the passage 36 resulting from the entry of the restrictor member 59 into the passage'insures deactuation of the impact pin 39 prior to the lowering of the casing 10 relative to the work member 28. Because the upper portion of the passage 36 is restricted by the restrictor member, the pressure release in the lower portion of the passage 36, the branch passage 37, the chamber 22 and the cylinder 38 is relatively slow and is not in any sense instantaneous. Therefore, the pressure within these enumerated elements falls below 60 pounds per square inch (using the example previously set out) and the impact pin 39 is thereby deactuated. The pressure then falls below 50 pounds per square inch and the casing 10 is lowered relative to the work member 28. Thus, there is no possibility of the pressure within the chamber 22 being released prior to deactuation of the impact pin 39 and this prevents any possibility of the hammer 20 impacting the tappet 23 to drive the work member 28 whereby the flange 29 of the work member may be driven against the impact pin 39, creating the danger of shearing ofl the impact pin. While the impact pin is designed to withstand impact against the flange 29 resulting from vibratory movement of the casing 10, it need not be designed to withstand the larger impact force resulting from a blow imparted thereto by the hammer 20.

The impact pin 39 and its positioning relative to the retainer member 31 plays an important part in the successful operation of the invention. As has been previously brought out, it is desired that the impact pin substantially abut the retaining flange 29 of the work member when the casing is raised relative to the work member. This position achieves full utilization of the forces causing the easing 10 to vibrate and these vibratory forces are translated into impact against the flange 29 without dissipation in the raising of the casing, with the result that the work member is more readily removed from the frictional grip of a material it has penetrated. The retaining member itself could not be used for this purpose because it would necessitate raising the retainer member upon the front head 10a of the casing until this desirable relationship were provided. Since the retainer member cannot have the ear 33 thereof move clear of the flange 29 during normal operation of the paving breaker, the impact transferred to the work member 28 from the hammer 20 would be evident as an impact between the flange 29 and car 33 of the retainer member, and since the force of this impact is extremely large the ear 33 would be broken upon receiving the force of this impact. It is essential, therefore, that the retainer member 31 be positioned upon the front head 10a in its usual position so that when the retaining flange 29 is engaging the car 33 the work member 28 is lowered to a point where it is incapable of receiving impact blows from the hammer 20 and tappet 23. The impact pin 39 must, then, be mounted above the ear 33 of the retainer member and preferably the specific relationship is as illustrated in the drawing.

It has been seen that my invention utilizes the vibratory motion of the paving breaker casing to effectuate the removal of the paving breaker work member from the frictional grip of a material it has penetrated. At the same time, it is no longer necessary for the workman to lift the heavy casing of the paving breaker during the pull out operation, since I provide selectively operable fluid pressure means to accomplish this result. Muscular fatigue of the workman is thereby minimized, with an accompanying increase in his general efficiency. The automatic lifting of the casing establishes the most desirable relative positioning of the casing and work member and maintains this positioning during the entire pull out operation, whereby the pull out is more effective and eflicient. The provision of the impact member and its timed actuation relative to the lifting of the casing of the paving breaker insures utilization of the entire forces causing the casing vibration to drive the work member from embedded position, while at the same time the impact pin and normal paving breaker elements are protected against breakage.

While'in the foregoing specification I have set forth a specific embodiment of myinvention in considerable de tail for purposes of illustration, it is evident that numerous changes may be made in the details by those skilled in the art without departing from the spirit of my invention.

I claim:

1. In a pneumatic paving breaker having an axially vibratory casing equipped with a work member constrained for limited axial movement with respect thereto and adapted upon operation of the breaker to penetrate a work material, said work member having the characteristic of sometimes being rigidly held by a frictional force developed between such penetrated material and the work member: means for producing a pneumatic force between the casing and work member continuously urging the casing away from the work material and being inferior to said frictional force and substantially in excess of the weight of the casing, and an impact member arranged with said casing and work member for rigidly arresting the vibratory movements of the casing in a direction away from the work material so as to produce a repetitious impact force acting upon the work member and of greater magnitude than said frictionalforce but inoperative to substantially restrict vibratorymovements of the casing toward the work material.

2. In a pneumatic paving breaker having an axially vibratory casing equipped with a work member constrained for limited axial movement with respect thereto and adapted upon operation of the breaker to penetrate a work material, said work member having the characteristic of sometimes being rigidly held by a frictional force developed between such penetrated material and the work member: a pedestal interposed between opposed areas of said work member and casing, means for producing a pneumatic force between said pedestal and casing to drive said pedestal into engagement with said work member and move said casing relative thereto, said pneumatic force being inferior to said frictional force and substantially in excess of the weight of the casing.

3. In a paving breaker structure having a vibratory casing, a work member constrained for limited axial movement relative to said casing and a tappet member movably mounted within said casing and being adapted to transfer impact blows to said work member, said work member being equipped with a laterally extending flange and having the characteristic of sometimes being rigidly held by a frictional force developed between it and a work material penetrated thereby, an impact pin movably carried in said casing, means for selectively actuating said impact pin to move the same adjacent said work member for engagement with said annular flange, fluid pressure means communicating with said casing adjacent said tappet member for developing a fluid pressure force between said tappet member and said casing of a magnitude in excess of the weight of the casing, and means for selectively actuating said fluid pressure means, said fluid pressure means when actuated being operative to raise said casing to bring said impact pin, when actuated, into substantial abutment with said annular flange whereby the vibratory movementsof said casing in one direction are rigidly arrested by the engagement of said impact pin with said annular flange, said impact pin being inoperative to arrest vibratory movement of said casing in the other direction.

4. In a pneumatic paving breaker having an axially vibratory casing equipped with a work member con strained for limited axial movement with respect thereto and adapted upon operation of the breaker to penetrate a work material, said work member having the characteristic of sometimes being rigidly held by a frictional force developed between such penetrated material and the work member: means for producing a pneumatic force between the casing and work member continuously urging the casing away from the work material and being inferior to said frictional force and substantially in excess of the weight of the casing, and selectively operable means arranged with said casing and work member for rigidly arresting the vibratory movements of the casing in theldirection awayfrom the work materialso as to produce a repetitious impact force acting upon the work member and of greater magnitude than said frictional force, but at the same time being inoperative to restrict vibratory movements of the casing in the opposite direction.

5. In a pneumatic paving breaker having an axially vibratory casing equipped with a work member constrained for limited axial movement with respect thereto and adapted upon operation of the breaker to penetrate a work material, said work member having the characteristic of sometimes being rigidly held by a frictional force developed between such penetrated material and the work member: means for selectively producing a pneumatic force between the casing and work member operative to continuously urge the casing away from the work material and being less than said frictional force and substantially in excess of the weight of the casing, and impact means carried by said casing for impact engagement with said work member and being selectively operable for rigidly arresting the vibratory movements of the casing in the direction away from the work material so as to produce a repetitious impact force acting upon the work member and of greater magnitude than said frictional force, but inoperative to arrest the vibratory movements of the casing in the opposite direction.

6. In a percussive tool having a vibratory casing equipped: with a work member constrained for limited axial movement with respect thereto and adapted upon operation of [the breaker to penetrate a work material, said work material having the characteristic of sometimes being rigidly held by a frictional force developed between such penetrated material and the work member: means for producing a force operative between the casing and work member for urging the casing away from the work material and being inferior to said frictional force and in excess of the weight of the casing, and selectively operable means arranged with said casing for operable engagement with the work member for rigidly arresting the vibratory movements of the casing in a direction away from: the work material so as to produce a repetitious impact force acting upon the work member and of greater magnitude than said frictional force but being inoperative to arrest the vibratory movements of the casing in the other direction. l

7. In a pneumatic paving breaker having an axially vibratory casing equipped with a work member constrained for limited axial movement with respect thereto and adapted upon operation of the breaker to penetrate a work material, said work member having the characteristic of sometimes being rigidly held by a frictional force developed between such penetrated material and the work member: means for selectively producing a pneumatic force between the casing and work member continuously urging the casing away from the work material and being substantially in excess of the weight of the casing, and an impact member carried by said casing for selective actuation and, when actuated, arranged with said work member for rigidly arresting the vibratory movements of the casing in a direction away from the work material so as to produce a repetitious impact force acting upon the work member of greater magnitude than said frictional force.

8. In a pneumatic paving breaker having an axially vibratory casing equipped with a work member constrained for limited axial movement with respect thereto and adapted upon operation of the breaker to penetrate a work material, said work member having the characteristic of sometimes being rigidly held by a frictional force developed between such penetrated material and the work member: means for producing a pneumatic force between the casing and work member continuously urging the casing away from the work material and being inferior to. said frictional force and; substantially in excess of the Weight, of the casing, a cylinder carried by said casing, an impact pin slidably mounted therein, means for selectively providing a pneumatic pressure to said cylinder for actuating said pin, and resilient means for biasing said pin in normally inoperative condition, said pin being arranged when actuated for operative engagement with said work member for rigidly arresting the vibratory movements of said casing in a, direction away from the work material so as to produce a repetitious impact force acting upon the work member and of greater magnitude than said frictional force.

9. In a .pneumatic paving breaker having an axially vibratory casing equipped with a work. member constrained for limited axial movement with respect thereto and adapted. upon operation of the breaker to penetrate a work material, said work member having the characteristic of sometimes being rigidly held by a frictional force developed between such penetrated material and the work member: a pedestal interposed between opposed areas of said work member and casing, means for producing a pneumatic force between said pedestal and casing to drive said pedestal into engagement with said Work member and to lift said casing thereon, and means arranged with said casing and work member for rigidly arresting the vibratory movements of the casing in the direction away from the Work material so as to produce a repetitious impact force acting upon the work member and of greater magnitude than said frictional force.

10. In pneumatic paving breaker having anaxially vibratory casing equipped with a work member constrained for limited axial movement with respect thereto and adapted upon operation of the breaker to penetrate a Work material, said casing providing a chamber therein adjacent the inner end of said work'member adapted to receive the inner end of said work member therein, said Work member having the characteristic of sometimes being rigidly held by a frictional force developed between such penetrated material and the work member: an impact transferring member movably mounted in said chamber and adapted to engage the inner end of said work member, means for producing a pneumatic force operative between said impact transferring member and a surface of said casing removed from said work member for urging the casing away from the work material, said pneumatic force being inferior to said frictional force and in excess of the weight of the casing, and means arranged with said casing and work member for, selectively, rigidly arresting the vibratory movements of the casing away from the work material so as to produce a repetitious impact force acting upon the work member and of greater magnitude than said frictional force.

11. In a pneumatic paving breaker having an axially vibratory casing equipped with a work member constrained for limited axial movement with respect thereto and adapted upon operation of the breaker to penetrate a work material, said work member having the characteristic of sometimes being rigidly held by a frictional force developed between such penetrated material and the work member, said casing providing a tappet chamber therein adapted to receive the inner end of said work member, and a tappet movably mounted in said chamber: said casing providing a flow passage communicating at one end with a source of pneumatic pressure fluid and at its other end with said tappet chamber so that a pneumatic force can be selectively provided that is operative between the casing and tappet to move said tappet against the inner end of said work member and urge said casing in a direction away from the work material, said pneumatic force being inferior to said frictional force and substantially in excess of the weight of the casing, and means arranged with said casing and work member for selective actuation for rigidly arresting when actuated the vibratory movements of the casing away from the work material by engagement with aid work member so as to produce a repetitious impact force acting upon the worker member of greater magnitude than said frictional force.

12. In a pneumatic paving breaker having an axially vibratory casing equipped with a work member constrained for limited axial movement with respect thereto and adapted upon operation of the breaker to penetrate a work material, said work member having the characteristic of sometimes being rigidly held by a frictional force developed between such penetrated material and the work member: an impact member carried by said casing and, when actuated, arranged with said work member for operative engagement therewith for rigidly arresting the vibratory movements of the casing in a direction away from the work material so as to produce a repetitious impact force acting upon the work member and of greater magnitude than said frictional force but inoperative to arrest the vibratory movements of the casing in the direction toward said work material.

13. The structure of claim 7 in which said impact member is normally biased in an inoperative position, and means are provided for selectively actuating said impact member.

14. The structure of claim 7 in which means for actuating said impact member are pneumatic.

15. The structure of claim 8 in which said work memher is equipped with an enlargement adapted to be engaged by said pin for rigidly arresting the vibratory movements of said casing.

16. The structure of claim 9 in which a valve-controlled passage communicates atone end with a source of pneumatic pressure fluid and at its other end with the space defined between said pedestal and said opposed area of said casing for providing said pneumatic force therebetween.

17. In combination with a tool having a work member adapted upon operation of the tool to penetrate and be frictionally gripped by a work material and having also a casing structure providing a mounting for the work member and vibrating relative thereto during operation of the tool, means developing a force arresting the vibratory movement of said casing in one direction relative to said work member when that member is frictionally gripped in a work material, said meanscomprising a pneumatic cushion operative, in effect, between said work member and casing to limit said force to a value normally less than the holding force applied to said work member by such frictional grip.

18. The combination of claim 17 in which said pneumatic cushion comprises a fluid pressure operative to limit said force to a value inferior to the intermittently active force. that causes downward vibration of the casing.

19. The combination of claim 17 in which said pneumatic cushion comprises a fluid pressure operative to limit said force to a value less than the sum of the intermittently active force causing downward vibration of the casing and the weight of the casing.

20. The combination of claim 17 in which said force has a value. substantially greater than the weight of said casing.

References Cited in the file of this patent UNITED STATES PATENTS Curtis Oct. 30, 1951 

